Hi i need to differentiate the following function:

f(x) = e^x . (x+2) . (x-1)

I know the answer is

f'(x) = e^x (x^2 + 3x -1)

But have no idea how to get to this! Any help please?

Printable View

- Dec 16th 2009, 11:19 AMxxJaRxxDifferentiation
Hi i need to differentiate the following function:

f(x) = e^x . (x+2) . (x-1)

I know the answer is

f'(x) = e^x (x^2 + 3x -1)

But have no idea how to get to this! Any help please? - Dec 16th 2009, 11:30 AMxxJaRxx
Plus then i need to make f'(x) = 0 and find that x = -3.30 and x = 0.30 :\

- Dec 16th 2009, 11:44 AMadkinsjr
I think the function looks like this:

$\displaystyle f(x)=e^{x(x+2)(x-1)}$

If I'm correct, then the derivative is $\displaystyle f'(x)=e^u\frac{du}{dx}$ where $\displaystyle u=x(x+2)(x-1)$. This is the chain rule.

It's difficult to read what you typed. You should try to use the latex. - Dec 16th 2009, 11:49 AMxxJaRxx
No sorry the question is

f(x) = (e^x) . (x+2) . (x-1)

and answer is

f'(x) = (e^x) (x^2 + 3x -1) - Dec 16th 2009, 12:04 PMpickslides
If the equation is $\displaystyle f(x) = e^x (x+2) (x-1)$

Then $\displaystyle f'(x) =\left[e^x \right]' (x+2) (x-1) +e^x \left[(x+2) (x-1)\right]'$ - Dec 16th 2009, 01:15 PMxxJaRxx
Thanks for everyones help ive got it sorted now!

Need help with this now!

Whats the derivative of:

Sin ( (x^2) + x ) - Dec 16th 2009, 01:20 PMpickslides
Lets say

$\displaystyle y = \sin( x^2 + x ) $ and $\displaystyle u = x^2 + x\implies y=\sin(u)$

Now $\displaystyle \frac{dy}{dx} = \frac{dy}{du}\times \frac{du}{dx}$ - Dec 16th 2009, 01:25 PMxxJaRxx
so the answer is..

(2x + 1) . cos( (x^2) + x )

Is that right? - Dec 16th 2009, 02:10 PMxxJaRxx
Okay so i swear the answer to this question is wrong!

Bit of integration instead of differentiation! :p

$\displaystyle \int3xsin(7-x) dx$

and the answer is

$\displaystyle 3xcos(7-x) + 3sin(7-x) + c$

Whereas I would have said it was

$\displaystyle 3xsin(7-x) - 3cos(7-x) + c$

Any help? - Dec 16th 2009, 03:15 PMpickslides
- Dec 16th 2009, 03:20 PMpickslides
Read this Integration by parts - Wikipedia, the free encyclopedia

For $\displaystyle \int uv' = uv - \int vu'$

In your case make $\displaystyle u=3x $ and $\displaystyle v' = \sin(7-x)$

now find $\displaystyle u'$ and $\displaystyle v$